A High Signal-to-Noise Spectrum of NGC 7469: New Support for
Reprocessing of Continuum Radiation
Gerard A. Kriss, Bradley M. Peterson, D. Michael Crenshaw,
and Wei Zheng, 2000, ApJ, 535, 38
From 1996 June 10 to 1996 July 29 the International AGN Watch monitored the Seyfert I galaxy NGC 7469 using the International Ultraviolet Explorer, the Rossi X-ray Timing Explorer and a network of ground-based observatories. On 1996 June 18, in the midst of this intensive monitoring period, we obtained a high signal-to- noise snapshot of the UV spectrum from 1150-3300 A using the Faint Object Spectrograph on the Hubble Space Telescope. This spectrum allows us to disentangle the UV continuum more accurately from the broad wings of the emission lines, to identify clean continuum windows free of contaminating emission and absorption, and to deblend line complexes such as Ly alpa +N V, C IV + He II + O III], Si III] + C III], and Mg II + Fe II. Using the FOS spectrum as a template, we have fit and extracted line and continuum fluxes from the IUE monitoring data. The cleaner continuum extractions confirm the discovery of time delays between the different UV continuum bands by Wanders et al. Our new measurements show delays increasing with wavelength for continuum bands centered at 1485 A, 1740 A and 1825 A relative to 1315 A with delays of 0.09, 0.28 and 0.36 days, respectively. Like many other Seyfert 1 galaxies, the UV spectrum of NGC 7469 shows intrinsic, blue-shifted absorption in Ly alpha, N V and C IV. Soft X-ray absorption is also visible in archival ASCA X-ray spectra. The strength of the UV absorption, however, is not compatible with a single-zone model in which the same material absorbs both the UV and X-ray light. Similar to other Seyfert galaxies such as NGC 3516, the UV-absorbing gas in NGC 7469 has a lower ionization parameter and column density than the X-ray absorbing material. While the UV and X-ray absorption does not arise in the same material, the frequent occurrence of both associated UV absorption and X-ray warm absorbers in the same galaxies suggests that the gas supply for each has a common origin.